The present invention relates to a method for installing a self-supporting tower for the extraction of hydrocarbons from a marine environment and to a tower thus installed.
The method seeks in particular to install self-supporting towers in very deep marine environments in order to extract the hydrocarbons present in the sea bed subsoil, and more specifically to raise these hydrocarbons from the sea bed to the surface.
Such self-supporting towers entail the use of long and also large diameter tubular pipes and, therefore, of bulky floats to keep them suspended vertically in the marine environment. To do this, an anchorage installation is first of all installed in the sea bed above the hydrocarbon-rich subsoil, then the float and the pipe are towed out on the surface by a ship to an installation zone situated substantially in line with the anchorage installation. The pipe is generally filled with air to improve its buoyancy and make it easier to transport, and is coupled to the float by one end so that the whole entity can be towed. Next, the pipe alone is progressively submerged while the float remains lying down on the surface. Also, the pipe is connected to the float by means of pivot members in order to allow the pipe to pivot from a horizontal position into a substantially vertical position. The free end of the pipe is then connected to a hauling line which is first stretched as far as the anchorage installation where it is engaged through return means then stretched back up to a surface ship. The surface ship then moves away from the installation zone causing the free end of the pipe to be made to move toward the anchorage installation. As a result, the float tips, pivoting about the end of the pipe as it gradually submerges. Also, the nearer the free end comes to the anchorage installation, the more the float becomes submerged. After the free end of the pipe has been coupled to the anchorage installation, the float applies an upthrust toward the surface, keeping the tubular pipe rising vertically from the anchorage installation.
Reference may be made to document FR 2 768 457 which describes such a method of installing a self-supporting tower.
However, as the depth of the marine subsoils exploited is becoming increasingly great, the risers and floats are respectively longer and bulkier and, as a result, the methods of installing the self-supporting towers are becoming increasingly complex.